Stress-induced C-terminal lysine acetylation of p53 plays an important role in the activity of p53 as a transcription factor that regulates cell cycle arrest, senescence or apoptosis. The long-term goal of this Project is to seek mechanistic understanding of the molecular interactions that regulate the tumor suppressor p53. While multiple acetylation sites in its C-terminal tail have been reported, specific effects of individual or combined acetylation of these lysine residues on p53 activity remain elusive. Preliminary data is presented involving the analysis of p53 function that acetylation-induced p53 activation in response to DMA damage is involved in co-activator recruitment. This study revealed that p53 recruitment of the co-activator CBP (CREB binding protein) requires association of the conserved bromodomain of CBP with p53 at acetylated Iys382: a specific molecular interaction that is essential for p53-induced transcriptional activation of the cyclin- dependent kinase inhibitor p21, involved in G1 cell cycle arrest. We hypothesize that distinct modifications of p53 C-terminal residues, including lysine acetylation and ubiquitination, as well as serine phosphorylation, have differential effects on p53 functions in cells under different conditions. A multifaceted approach is proposed to address mechanistic underpinnings of p53 transcriptional activation with the emphasis on the role of C-terminal post-translational modifications in p53 activation. To understand the complex molecular mechanisms underlying p53 regulation, I propose to investigate the dynamics of acetylation and molecular interactions of p53 involving its C-terminal lysines. Three specific aims are proposed to achieve this goal: (1) to investigate the kinetics of acetylation of the C-terminal lysines in p53 function in normal and tumor cell lines; (2) to elucidate the differential roles of the co-activators p300 and CBP in p53 regulation using CHIP and siRNAs; and (3) to modulate p53 activity between cell growth arrest and apoptosis using the newly developed CBP Bromodomain-binding small molecule inhibitors. The emerging results from the proposed studies are expected to enhance our understanding of the molecular basis of C-terminal modifications in p53 function. Given the central role of p53 in cancer, these studies will have important implications for the prognosis and treatment of human tumors. [unreadable] [unreadable] [unreadable]